“I think it’s all about your body and how you feel inside,” she tells The Post. “You can wake up and look at the mirror and say, ‘Oh my God, I feel so beautiful and hot, let me just wear sweatpants and walk on the street,’ and people are going to turn around and say, ‘She’s hot!’ because you’re feeling it inside.”

We should all be so lucky.

Sweats or no, the 28-year-old model is on fire. Shayk broke out in the States with the cover of the 2011 Sports Illustrated swimsuit issue, and she hasn’t let up since. She’s modeled for some of the biggest names in fashion — Armani Exchange, Guess, Lacoste. She’s appeared in the pages of every major magazine, and even starred in a Kanye West music video (“Power”).

Ronaldo has been nursing a knee injury, but is set to start against the US on Sunday.Photo: AP

But she’s not just sitting pretty on the sidelines this summer. Come July 25, she’ll make her acting debut in the blockbuster “Hercules,” opposite Dwayne “The Rock” Johnson. In the film, which sees the mighty Grecian half-god leading a group of mercenaries to end a civil war, Shayk stars as his wife, Megara.

Despite her years of being in front of the camera, Shayk found the new experience nerve-racking. “It’s completely different from modeling. Like, on model set, when you’re shooting a commercial, you can have 30 people on set behind the camera,” she says. “But on Paramount’s set, it was, like, 200 people. “So it was a little bit stressful,” she says, adding, “And it’s a lot of waiting in the trailer.”

Director Brett Ratner (“Rush Hour,” “X-Men: The Last Stand”) specifically sought out the Sports Illustrated swimsuit model. “When they sent me over the scenario,” she says, “I looked at it, and they say the role is very small. A small part — but it’s something I can handle, because I don’t have any experience to be in the movie. It was very unplanned. It just came along and I said, ‘Okay, let me try to do it.’ ”

That “just-go-for-it” attitude is what launched her A-list career to begin with. Born in a small Russian village to a coal miner and a pianist, Shayk (actual last name: Shaykhlislamova) didn’t have the most glamorous of childhoods.

“As a girl, I used to go to the garden and take care of the potatoes and cucumbers and tomatoes,” she says, cracking up. “So you see, if I finish my modeling career, I can work as a gardener easily.”

She was discovered after high school, when she enrolled in beauty school with her sister and was asked by the modeling school next door to participate in the “Miss Chelyabinsk” beauty pageant. She won.

Shayk walks the runway at amfAR’s 20th Annual Cinema Against AIDS fashion show in May 2013.Photo: Getty Images

“It’s such a joke. Miss Chelyabinsk — it’s a very small city,” she says. “It’s like a ‘Miss Village,’ you know?” Despite the lack of prestige, the pageant led her to getting a manager and moving to Paris. There, her early modeling days were no walk in the park. “I remember when I left my village, my mom gave me only like $10 or $15, because we didn’t have any money,” she says. “And then there was a lot of people who looked at me, like, ‘Oh, you’re not a model because you have dark skin. You have a little shape. You’re not skinny enough.’ It was really hard, but I’m Russian and I’m a Capricorn. I say to myself, I would never go back to Russia with nothing.”

And she didn’t. Shayk landed her first cover for a small Parisian magazine. Her career took her to Spain, then New York, where she’d land upon the job that would change her life forever. She began work with Sports Illustrated, and, in 2011, landed the coveted Swimsuit Issue cover, an honor previously held by top models such as Christie Brinkley, Cheryl Tiegs and Tyra Banks. And it’s not all just lying on a beach in a bikini. Nor is it always easy to look sexy. For the 2012 Swimsuit Issue, Shayk was pictured walking a cheetah (her pick over a zebra or a lion).

“It was crazy because a cheetah is the fastest animal in the world, and very strong, and I have to hold cheetah on leash,” she says. “I was trying to hold him on the leash and walk with the swimsuit, trying to make my face sexy and relaxed, but I was terrified. I was not walking cheetah — cheetah was walking me.”

She says that her photos for the magazine have been her biggest breakthrough. “Sports Illustrated, they launched my career in America. People know your name. You’re part of the legends,” she says. “And, of course, I got more offers and work. I think my small movie role is [because of] my Sports Illustrated cover as well.”

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Pilates, light weights and even boxing. “I do box, especially when I’m angry,” she says. “Oh my God, you better stay away. I’m turning into the very Russian woman.”

But, she’d like to point out, none of this means she doesn’t eat. “I love chicken nuggets from McDonald’s. Every time I’m at the airport, I always get chicken nuggets with extra BBQ sauce,” she says. “People think I’m getting paid to post chicken nuggets on Instagram. That’s so wrong. I just love chicken nuggets.”

She’s not the only one photographing herself in airports. In the years since her arrival in the public consciousness, Shayk has become a tabloid staple, hounded by paparazzi, in part because of her fantasy relationship with Ronaldo. She now splits time between New York and Madrid, where he lives. “The day you decide to become a public person, you have to learn how to deal with [it],” she says. “You can’t be mad at paparazzi and media because they’re doing their job.”

Ronaldo and Irina laugh during the Madrid Open in 2011.Photo: Reuters

She won’t, however, discuss her relationship with Ronaldo, other than to take a strong stand against being called a WAG. The often derogatory term is an acronym for “wives and girlfriends” of professional athletes, usually characterized as airheads who married for money and shop their days away.

“Let me tell you something,” she says. “I say, I’m a person and I have my career. I [have been] a model for more than eight years — I didn’t become a model because of someone or somehow. I worked very hard for my success. And I consider [myself to be] not a WAG or some other name. I consider [myself] to be a woman with her own career with her own independency.”

After promoting “Hercules,” Irina will enjoy some down time and also focus on her charity work helping kids in Russia. But she’s down for another movie part, and even has a pretty solid idea. “My dream role would be to play some Russian character in something like a James Bond movie,” she says. “Something crazy, because I think I’m crazy Russian.”

Irina’s greatest hits

Another reason to hate Ronaldo: His stunning model girlfriend

Cristiano Ronaldo faces competitors both on and off the field. “I love fishing,” says Shayk, seen here with her love in Thailand. “[But] if someone gets more fish, I want to push them out of the boat.”

*XPOSURE PHOTOS

In December Shayk posted this photo of herself planting a smooch on Ronaldo’s wax figure at the Museo de Cera de Madrid. As for which team she’s rooting for at the World Cup? “Oh, guess who?” she says playfully.

Instagram

For the Sochi Olympics, Shayk led the Russian team during the opening ceremonies’ Parade of Nations. “I didn’t believe [it when] they invited me,” she says. “It was a big responsibility.”

Getty Images

The couple posed for Spanish Vogue’s May cover, working with photographer Mario Testino. And how did she feel about Ronaldo stripping down while she kept covered? “Amazing!” she says, laughing. “Finally!”

Vogue

“[It’s] my biggest career accomplish-[ment],” Shayk says of this 2011 Sports Illustrated cover. “It’s still unbelievable. I have it on my coffee table. Every time I’m passing it, I’m like, ‘Wait a second — is it me?’”

Sports Illustrated

Shayk (with Panka Kovaks and Rufus Sewell) makes her acting debut in “Hercules.” The experience was nerve-racking: “[It can make] you feel very insecure.”